Democratic Congressional Campaign Committee Chairman Ben Ray Luján expressed confidence Thursday his party will take control of the House, but he remains concerned about the impact of outside Republican money and gerrymandered districts.

“As far as what keeps me up at night, Republicans have committed what seems like unlimited amounts of money to these elections,” the New Mexico Democrat told reporters Thursday. “We’re seeing Super PAC after Super PAC on the Republican side continue to tear in.”

Luján said the other challenge for Democrats involves congressional maps drawn to favor Republicans — a concern shared by his predecessor, former New York Democratic Rep. Steve Israel.

Luján said his party is still in a strong position for a net gain of 23 seats to take over the House, pointing to candidates with compelling personal profiles who are connecting with voters.

The main Republican Super PAC focused on House races, the Congressional Leadership Fund, has reported record fundraising totals this election cycle. The group launched television ads in a slew of competitive districts starting in early August in an effort to define first-time Democratic candidates early on in the general election campaign.

But Luján said he had not seen much evidence that early advertising was making an impact in those races.

“While CLF was up and aggressive and early, how much of that resonated with voters?” Luján said. “The polling shows that our candidates that were receiving the onslaught of those attacks, for the most part came out of there without the numbers moving against them.”

Democrats were aware from the start of the cycle that outside GOP groups would outspend Democrats in these races, Luján said. So the committee focused on boosting its small-dollar fundraising, he said, training candidates early on, and sending field organizers to competitive districts in early 2017.

There was a focus on candidates’ own fundraising, Luján said. Democratic challengers have proven to be strong fundraisers, even outraising GOP incumbents in a few dozen contests.

“It’s sounding the alarms everywhere that we can,” Luján said. “We know that we don’t have to outraise them. We have always been smarter and more agile with our investments and we will continue to be.”

While the DCCC chairman predicted Democrats would win back the House, he expected many races to be close. He speculated that control of the House might not be known on Election Night, citing the impact of mail-in ballots in California and Washington, and states where close margins prompt recounts.

“I know that there will be a lot of close elections across America, elections that will be decided by less than 1,000 votes, each of which will determine who’s in the majority of the House of Representatives,” Luján said.

Luján also took questions on broader Democratic messaging. Health care remains the top issue for voters, he said, but the party will also highlight the stories of two GOP congressmen who have recently been indicted and those lawmakers facing ethics concerns.

GOP Reps. Chris Collins of New York and Duncan Hunter of California were both indicted last month, and both represent heavily Republican districts. But those recent developments demonstrate the importance of making sure strong Democratic challengers are competing in every district, Luján said.

Democrats would likely work on an infrastructure package, lowering the cost of prescription drugs and addressing stagnant and decreasing wages should they retake the House, Luján said.

Democrats need to focus on an economic agenda rather than talking about President Donald Trump, the chairman said. Midterm elections are often viewed as referenda on the current president, but Luján said candidates don’t have to talk about Trump because the president brings enough attention to himself.

But he did say Trump’s tweets Thursday about the death toll in Puerto Rico following Hurricane Maria were evidence that the country needs a strong legislative branch to act as a check and balance.

Trump tweeted that Democrats were distorting the death toll to undermine his presidency.